This invention relates to a process for producing a multilayer wiring structure for use in electronic circuit parts such as semiconductor-base integrated circuits, bubble memories, and the like.
For the production of multilayer wiring structures in semiconductor-base integrated circuits and the like, there has hitherto been used a process which comprises forming an interlayer insulating film of SiO.sub.2, SiN, or the like on a substrate supporting a patterned wiring layer, by a vapor growth method such as a vacuum deposition method, a CVD (chemical vapor deposition) method, or the like, and making through-holes in the substrate, followed by forming an upper wiring layer. However, the process comprising the formation of an interlayer insulating film by the vapor growth method has suffered from the following problem: As shown in FIG. 3 of the accompanying drawings, level differences of an underlying wiring layer 2 are retained as they are even after the formation of an interlayer insulating film 3, and when an upper wiring layer 4 is formed, its portions on steep sides of the above-mentioned level differences become extremely thin, which results in readily breaking the wiring. In FIG. 3, numeral 1 represents a substrate.
To solve this problem, there has been proposed and practically used a process which comprises forming an interlayer insulating film by applying a solution of a poly(amic acid) produced from an aromatic diamine and an aromatic tetracarboxylic dianhydride, and curing the applied poly(amic acid)(Japanese Patent Examined Publication No. 44871/76).
In recent years, however, the degree of integration in electronic parts including semiconductor-base integrated circuits is increased remarkably, the number of superposed wiring layers is also more multiplied, and thus the necessity of flatting the wiring level differences is further increasing. The above-mentioned poly(amic acid) produced from an aromatic diamine and an aromatic tetracarboxylic dianhydride has very low solubility even in solvents for poly(amic acid)s and consequently it is impossible to prepare concentrated solutions of this poly(amic acid). Therefore, the flatting of the above-mentioned wiring level differences is unsatisfactory with such a poly(amic acid) and multilayer wiring structures of two or more layers have been difficult to produce.